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Homeowner Control Measures
Gypsy Moth defoliationHow much a homeowner can do to mitigate against gypsy moth depends on a number of factors:
  1. The size of the wooded area and the number of trees in the area. Dealing with 2 trees may be straightforward, 20 somewhat more difficult but 200 will probably be outside the scope of a homeowner with no special equipment.
  2. The severity of the outbreak. At the peak of an outbreak, the hatch from a vast number of egg masses and the amount of blow-in young caterpillars may overwhelm many control measures. Also, the behavior of caterpillars changes when they reach very high population levels, making them less accessible to control.
  3. The type of measures used. Not much has changed in what is available to the homeowner until recently, when a novel form of encapsulated pesticide has become available.

The control measures are listed in terms of chronology, starting with egg masses (which are present for at least 8 months), through the caterpillar and adult stages.


August to Mid April: Egg MassesGypsy Moth egg masses
 
Egg Mass Destruction

An egg mass produced by a healthy gypsy moth contains between 500 and 1,000 eggs, most of which will hatch into caterpillars!

How: Scrape them off into a container and burn them or soak them in dilute detergent for a few days.

They can also be sprayed in place with a horticultural oil (available at lawn or garden centers). Spray the oil onto the egg mass until it is soaked.

Avoid: Scraping them onto the ground - where they could still survive. Stamping on them with your feet will still result in many survivors.

Also avoid damaging the tree bark in any way - by using any harsh products (like cleaning products or motor oil) on the tree

Unless your property is unique, don't keep egg masses in place because you have heard that somebody needs to come and count them. There are many more locations and trees in a county than a thousand local government personnel could count!

Does it Work? Scraping off egg masses is a good idea under most circumstances, especially at low population levels (say 250 egg masses per acre). You prevent 500 - 1,000 caterpillars from hatching for each egg mass destroyed.

Remember that gypsy moth get onto your property in two ways - from the egg masses on the trees on your property and from 1st stage larvae blowing in from up to several miles away. So clearing away all visible egg masses from your small apple trees for example would be advisable, but your job would not end there, as there could still be some blown-in larvae that would have to be controlled.

The main problem with scraping is the very limited accessibility of egg masses even in small trees, let alone 100ft oaks.


Mid-April to Early July: Caterpillars Adult Caterpillar

Control of caterpillars is most effective in the first 3 or 4 weeks after they emerge from egg masses. Bear in mind that their appetite is very much proportional to their size and that most of the defoliation damage will occur with the final 5th and 6th larval stages. Controls can be insecticidal or mechanical, such as physical barriers. Many insecticides work best on the 2nd and 3rd stage caterpillars, but lose their effectives on older larvae. The vast majority of insecticidal treatments are done with aircraft or specialized ground spray equipment that is beyond the reach of the homeowner.

Insecticidal Controls

Insecticide Spraying
If you choose to use pesticides to control the caterpillars, they must be applied at this time. There are two options: biological and chemical pesticides. For assistance in applying insecticides, consider contacting a certified arborist.

Biological pesticides
The most common treatment used against gypsy moth is a spray of Bacillus thuringiensis, commonly called Bt. (This is the same bacterial insecticide that the state sprays in its aerial programs.) It kills caterpillars that eat it within a week of its application. Bt causes the cells of the caterpillar's stomach lining to rupture. Bt is found naturally in soil and degrades within a week when exposed to sunlight. The variety of Bt used against the gypsy moth only affects caterpillars of moths and butterflies. Bt has no affect on animals, birds, people, or even other insects. It is sold under various labels (Bactur, Dipel, Foray, and Thuricide, to name a few). Bt must be applied to trees in May when caterpillars are less than 1/2-inch long. Timing is critical as Bt is significantly less effective on 4th stage and older caterpillars.

Because Bt has no known toxic effect on any vertebrate species, it is safe to apply as long as you take reasonable precautions. Remember that it has NO contact effect, so spraying it on bark will only be a waste of money; it has to be sprayed on leaves on which caterpillars are feeding.

Chemical insecticides
Numerous insecticides are registered against gypsy moth in Pennsylvania. Many products are available at your local garden center or nursery. Check the label to make sure gypsy moths are listed. Acephate (sold as Orhene), carbaryl (sold as Sevin), and malathion (sometimes sold as Cythion) are the most common active ingredients and are available in several formulations. If you elect to use a chemical insecticide, consider the potential impact on beneficial insects and natural enemies such as predators, parasites, and honeybees.

Remember that the label is a legal document! You must ALWAYS read and precisely follow the label directions. Our advice is to leave the application of chemical insecticide to the professionals.

Does it Work? As with so many homeowner control measures relating to trees, reaching the tops (and the middle) of those high trees is darned near impossible for the homeowner.

However, if you have a number of 8-foot high apple trees in your back yard, there is no reason why you should not have a high degree of success. But you shouldn't take that success for granted; a week or two after spraying the caterpillars could be back, so stay alert!

Barrier Methods
Barrier methods simply work as physical blocks to prevent caterpillars from climbing trees. These may be rigid barriers that larvae can't crawl over, or a barrier band covered with a sticky substrate that traps the caterpillars and deters their further movement. One supplier of these methods is TangleFoot. [http://pestcontrol-solutions.com/treeguard.htm] Barrier bands will prevent caterpillars from climbing back into trees after ballooning or when they have fallen to the ground.

Barrier bands can be made using duct tape or other nonporous material that can be wrapped around a tree trunk and coated with a commercially available sticky material such as TangleFoot®. NEVER put sticky material directly on the tree trunk. On thin-barked trees, tie butcher paper or paper bags around the trunk before using the duct tape. The sticky material may need to be re-applied periodically due to rain and other environmental conditions as well as when the bands are covered with caterpillars.

A variation of a barrier method is the burlap fold, also known as a Collection Band. It can be made from medium-weight dark cloth or burlap approximately 12–18 inches wide and long enough to completely wrap around a tree. Using a piece of cord or twine, fasten the middle of the cloth band to the trunk at chest height. Fold the top half of the cloth down to cover the bottom half. Older caterpillars are attracted to these "skirts" when looking for a place to hide during the day. You must remove and destroy the caterpillars each day, or several times a day during major outbreaks.

Susan's Method

Here's a fast-and-cheap method from Susan, a local resident who says it works very well for second stage and older caterpillars:

Material: 2-inch wide brown plastic package sealing tape (very cheap to buy)

Method: Tape a band around the tree with the sticky side to the tree, overlapping the tape an inch or two at the ends. You can use a push-pin to hold the free end temporarily. Then double the tape back (sticky side out) and band the tree with at least two slightly overlapping sticky-side-out levels of tape (which gives you a band 3½ inches wide).

The caterpillars congregate at the edges of the band and can be manually removed into a container for disposal several times a day.

Does it Work?
Barrier methods can work in light infestations, but they generally are not a 'fix & forget' kind of method. If you have a couple of acres of trees, you will have to inspect all the barriers regularly – and it can be quite an effort. For 4th stage larvae, collection bands will have to be emptied of caterpillars at least once a day.

The efficacy of barrier methods decreases with extremely high gypsy moth populations, because caterpillar behavior changes and older ones remain in the treetops without descending during the day.


Mid July - August: Pupae & Adults Adult Male Gypsy Moth

At this stage it is way too late to do anything about the current year's damage. The caterpillars went through all their development stages while feeding on your leaves and have pupated into brown pupae from which the adult moths will emerge. What measures you can take will all be directed against next year's gypsy moth outbreak.

Pupa Removal
The pupae are often found high above the ground under tree limbs where they are difficult to remove. So should you try and remove them? By all means remove and destroy any that are within reach, but as a major control measure, pupa removal would have marginal effect on the adult moth population.

Use of pheromone traps for adult moths
The flightless gypsy moth female moth attracts her mate by secreting a pheromone – a scent that the flying male moth homes in on. That same chemical can be manufactured and placed in a cardboard trap to attract males and kill them, thereby reducing the number of available males.

However, the PA Bureau of Forestry is advising homeowners against buying and using pheromone traps during a gypsy moth outbreak. The traps may serve to attract a higher number of males than otherwise would be present around the trap, thereby increasing the likelihood that a female will find a mate.

Does it work? No! Unfortunately, the gypsy moths, once they are in the adult stage, are pretty much beyond any sensible control method that we can use.


Aerial Applicators and Ground Spray Companies
There are many situations when homeowners or landowners are not able to do gypsy moth control measures themselves. These usually occur when either a small number of prized trees close to a house are being defoliated, or a forested area typically over 20 acres in size is being threatened by gypsy moths.

The small-scale situation would be handled by a ground spray company which would use high pressure sprays to target individual trees. The large-scale situation would be handled by an aerial applicator that operates helicopters or fixed wing aircraft.

The least well-served homeowner group is one that has forested areas ranging in size from 0.5 acre to 10 acres; this area is generally too big (and expensive) to be treated by a ground-spray company but too small to be treated by an aerial applicator.

Aerial Applicators
The DCNR gypsy moth spray program is aimed at forested residential areas. The limit of spraying does not extend beyond 500 feet from a residence or cabin located in the woods. So owners of forested parcels have to make their own private arrangements with aerial applicator companies. (There is a PA Forest Stewardship program] which offers some cost sharing for gypsy moth spraying, but according to participants, funds for spraying are rarely available.)

The PA DCNR publishes a list of aerial applicators who have stated that they can spray gypsy moths in PA. Click here to go to the list. The DCNR list offers a wide range of applicators ranging from established PA companies with long track records of gypsy moth spraying to out-of-state companies who are just getting started in forestry spraying. As with any professional service provider, it is a good idea to seek recommendations and referrals from landowners who have used their services in the past. Look for established addresses, web sites and be sure to Google company names to see what comes up!

Helicopters and Airplanes
The popular idea of a spray helicopter is that of a large flying fan blowing spray droplets deep into a forest canopy. This is a totally false notion! Once a helicopter goes into its translational flight at a medium forward speed, the turbulent wake (which affects the spray droplets) is very similar to that of a fixed-wing airplane.

In general, helicopters can spray small spray blocks more efficiently as they can change direction far more rapidly than an airplane. They begin to lose out on larger spray blocks as the faster speeds and larger hopper capacities of fixed wing aircraft result in a lower application cost per acre. But as for the quality of the deposit on the leaves? The helicopter one looks pretty much the same as an airplane one.

Size of Spray Block
The price per acre charged by aerial applicators varies according to its size due to an economy of scale obtained with larger blocks. The minimum acreage that an aerial applicator will spray varies from around 20 to 50 acres, but you can always negotiate with them if you have a smaller acreage (this would mainly apply to applicators operating helicopters).

Ground Application
Unlike aerial application, which uses volume rates of 0.5-1.0 gallon/acre, ground applicators use very high volume applications of dilute pesticide, often 50 gallons or more for each large tree. Smaller trees such as those found in apple orchards can be sprayed with lower volumes.

As far as we are aware, there are only two companies performing ground spraying in Centre County which can reach trees up to 100 feet in size, Meek Tree Service & Bartlett Tree Experts. If you are aware of other companies providing this service, please ask them to contact the Gypsy Moth Coordinator so that the list can be updated.

  • Meek Tree Service: (814) 355-0538
  • Bartlett Tree Experts: (814) 235-9228
*There are several companies that can spray smaller trees that are listed in the Yellow Pages.